1. Field of the Invention
The present invention relates to a power supply system having a battery that can be used by repeated charging/discharging (secondary battery), more particularly, to a power supply system having a protection facility against abnormal charging.
2. Background of Related Art
In various devices and apparatuses (such as notebook-sized personal computers (notebook PCs), PDAs, information terminal equipment including mobile phones, Mini Disc (MD) drives, and video cameras), secondary batteries are extensively employed as a battery that can be used many times by repeated charging/discharging. As a secondary battery, often nickel-hydrogen batteries or nickel-cadmium batteries are used, where such use is employed typically since these types of batteries are inexpensive and have larger capacity. Additionally, other types including lithium ion batteries, having higher energy density per unit weight than the nickel-cadmium batteries, and lithium-polymer batteries, that uses a solid polymer instead of a liquid electrolyte, may also be used.
If a secondary battery such as a nickel-hydrogen battery, a nickel-cadmium battery, a lithium ion battery, or a lithium-polymer battery, is in an over-charging state or an over-discharging state, problems such as lowered performance, damaged electrodes, or short-circuits inside the battery may occur.
For example, in Published Unexamined Patent Application No. 6-86469 (Japan Patent Office) the specification discloses a technique for the alarming of short-circuits by generating signals based on the detection of a lowered battery voltage and short-circuits within the battery. Additionally, in Published Unexamined Patent Application No. 2000-102185 Japan Patent Office), the specification discloses a technique wherein each secondary battery cell in a first battery group and each secondary battery cell in a second battery group are connected separately for monitoring/controlling purposes, such that if an internal short-circuit occurs in one of the battery groups, a short-circuit current is prevented from flowing into the secondary battery cells in the other battery group.
However, in above-referenced Published Unexamined Patent Application Nos. 6-86469 and 2000-102185 described above and incorporated by reference herein, when an internal short circuit occurs in a condition where the battery is charged to a voltage above a predetermined voltage due to a malfunction of the apparatus, it is impossible to prevent a battery from being in a dangerous state while short-circuit current can be prevented from flowing into batteries. As a result, it is generally known that when an internal short-circuit in a battery cell occurs in addition to overvoltage in the battery, the condition of the battery becomes dangerous.
In order to charge a secondary battery (battery-pack) a charger is often used with an alternating current (AC) adapter. When a short-circuit breakdown occurs in either a switching transistor in the charger or a short-circuit prevention transistor for preventing short-circuit in the charger, the AC adapter and the battery short-circuit electrically, resulting in an abnormal charging of the battery (first error). In this case, charging continues until a primary protection circuit in the battery pack goes into operation. At this point, the battery voltage, for example in the case of lithium-ion battery, is about 4.35 V/cell. If additionally a short-circuit occurs in the battery cell, a dangerous state (second error) is possible. These dangerous states as well as a situation where the battery is in a high temperature environment should be taken into consideration in designing.
Currently, intelligent batteries having a CPU built-in in a battery pack (secondary battery) are widely used. For example, a lithium ion battery constituting an intelligent battery is used, in which a charging stop FET (charging protection circuit) and a discharging stop FET (discharging protection circuit) are built in a battery pack. The CPU in the battery pack monitors the voltage in the battery by inputting a signal from a voltage detection circuit, then analog-to-digital (A/D) converting the signal inside it. In this battery pack, when the voltage reached 4.35 V or higher, for example, it is determined that abnormal charging occurs, and the charging is aborted by turning off the charging stop FET. Since the battery voltage in full charging (100% charging) state is 4.2 V (xc2x150 mV), the current design in which abnormal charging is detected at 4.35 V/cell is considered to be proper taking detection error and other factors into consideration.
However, while a safety state can be maintained in a normal condition, a dangerous state becomes possible, when in a condition charged to 4.35 V further occurs a malfunction such as internal short-circuit in the battery cell. It is therefore necessary to accommodate the worst case taking conditions such as ambient temperature into consideration.
The present invention is made to solve and overcome the technical problems described above, as well as other known limitations in the art. It is an object of the present invention to provide a battery, which is safer, even where double accidental malfunctions occur.
An object of the present invention is to operates to maintain safety, such that when a short-circuit occurs in a battery cell, and when the battery is charged to a voltage above a predetermined voltage due to a malfunction of a connected charger (or a portion of an apparatus), to above charging by detecting a malfunction of the charger (or the portion of the device) before the conventional first overvoltage protection facility is activated.
Therefore, in one aspect, the present invention is a power supply system with a battery for supplying power to a main system, comprising: charging current measuring means for measuring charging current for the battery; battery capacity calculation means for calculating (integrating) battery capacity of the battery; detection means for detecting malfunction occurring in the battery based on a charging current value obtained and the battery capacity calculated (malfunction occurrence detection means); protection facility activating means for activating a protection facility based on detection of malfunction occurrence; and notification means for notifying the main system of malfunction occurrence based on detection of the malfunction.
The detection means (malfunction occurrence detection means) is preferably adapted, for example, to detect malfunction occurrence based on information in a table for malfunction detection, showing the relation between battery capacity and malfunction detection current value. The detection means can also be adapted to detect malfunction occurrence based on an equation representing the relation between battery capacity and charging current value, which equation is separately defined according to battery capacity.
In another aspect, the present invention is also a computer device, comprising: a main system for data processing; and an intelligent battery for supplying power to the main system, wherein the intelligent battery comprises: a battery cell for charging and discharging; a current detection circuit for detecting charging current for the battery cell; a CPU for calculating battery capacity by integrating detected charging current, and recognizing malfunction occurrence occurring in the battery based on charging current value detected by the current detection circuit and the battery capacity calculated; and a protection circuit for performing stop operation according to instruction from the CPU based on recognition of malfunction by the CPU.
In a further aspect, the present invention may also be understood to be a battery connected to a main system of a computer device or the like (intelligent battery). Thus, a battery according to the present invention, comprises: a battery cell; a voltage detection circuit for detecting voltage for the battery cell; a current detection circuit for detecting charging current for the battery cell; a charging stop unit for stopping charging for the battery cell; and a control unit for activating the charging stop unit based on voltage detected by the voltage detection circuit, wherein before the voltage reaches a voltage for activating the charging stop unit, the control unit detects an abnormal state based on a charging current value detected by the current detection circuit, and activates the charging stop unit.
In another aspect, the present invention is a method for protecting a battery from abnormal charging, comprising: measuring a charging current value for the battery; calculating integrated capacity for the battery; and activating a protection facility when the charging current value measured for the calculated integrated capacity is larger than a predetermined value. The method is preferably characterized in that the protection facility is activated based on information such as table information or an equation, specifying a reference value representing a charging current value at which a malfunction is detected for an integration capacity, since malfunction occurring can be detected as soon as abnormal current for an integrated capacity flows. The protection method can also provide a battery with excellent safety since the protection facility can be activated in the state where the integrated capacity is less than 100%.
In another aspect, a method for protecting from abnormal charging according to the present invention is characterized for example, in that it comprises: recognizing that a battery is connected to an apparatus such as a typical notebook PC with a charger for constant-current/constant-voltage charging, by using ID or the like that is identification information delivered from the apparatus; measuring charging current value when the battery is charged while switching from constant-current charging to constant-voltage charging, determining based on the measured charging current value whether abnormal charging occurs or not; and aborting charging when it is determined that abnormal charging occurs.
In yet another aspect, the present invention may also be understood as programs for enabling in a microcomputer contained a battery to perform each of these functions. The programs can be provided to a microcomputer a processing unit from a remote program transmission device via a network, for example. The program transmission device may be configured to comprise storage means such as a CD-ROM, a DVD, a memory or a hard-disc with the programs stored therein, and a transmission means for reading the programs from the storage means and transmitting the programs to a device for executing the programs, via connectors and networks such as Internet or LAN. The programs may be provided by using a storage medium such as CD-ROM.